User:Amy Kerzmann/Sandbox 2

Voltage-gated Potassium Channel
Backgound

This crystal structure illuminated the principles of ion selectivity when it was solved in 1998. To further demonstrate the importance of this structure, the 2003 Nobel Prize in Chemistry was awarded to the principal investigator, Roderick MacKinnon.

Channel Structure:



The potassium channel is almost entirely buried within the lipid bilayer, which is evident when the hydrophobicity /scene> of each sidechain is mapped onto the structure (hydrophobic residues are shown in grey and hydrophilic in purple.)

The potassium channel is a homotetramer, meaning that it is comprised of four identical protein chains or monomers. Each monomer is predominantly alpha helical, with no beta strands. When viewed in N->C color coding (where the N-terminus is blue and the C-terminus is red), one can see that both termini are located on the cytosolic side of the membrane. The central core of the potassium channel is comprised of the two C-terminal helices from each monomeric subunit; the region of the protein between the second and third helices lines the cavity and makes contacts with potassium ions.

The central core of this protein is comprised of eight helices, two from each monomeric subunit. Since each monomer has the same orientation in the membrane, the protein has a four-fold rotational symmetry when viewed from the membrane surface. As a result, each of the channel-lining residues appears as a ring of four identical sidechains. This principle is represented by the conserved tyrosine residues that function as selectivity filters within the cavity. Additional aspartate and threonine residues line the channel. Looking at a composite of these residues, one can see that some hydrophobic patches remain within the cavity.

Channel Function:

Here's how it works.

References